BEIRUT — The international envoy working to end Syria’s civil war warned Sunday that the failure of the government and the rebels to pursue a political solution could lead to the ‘‘full collapse of the Syrian state’’ and threaten the world’s security.

Lakhdar Brahimi, who represents the United Nations and the Arab League, said that as many as 100,000 people could be killed in the next year as Syria moves toward ‘‘Somalization’’ and rule by warlords.